diff --git a/2bit.py b/2bit.py
index 7346f6e..1789fc7 100644
--- a/2bit.py
+++ b/2bit.py
@@ -12,7 +12,12 @@ def format_dither(d):
     d = float(int(float(dither) * 1000)) / 10
     return str(d) + "%"
 def auto_dither(bits):
-    return 1.0 / (bits + 1)
+    #return 1.0 / (bits + 1)
+    return 1.0 / (2**bits)
+def auto_counter_max(w):
+    k = max(int(float(w)/200),2)
+    while w % (k + 1) == 0: k += 1
+    return k
 if len(sys.argv) >= 3:
     outfile = sys.argv[2]
 if len(sys.argv) >= 4:
@@ -29,8 +34,14 @@ if dither > 1:
     dither /= 100
 per_color = "--per-color" in args
 use_non_random_dither = "--non-random-dither" in args
+image = PIL.Image.open(sys.argv[1])
 if use_non_random_dither:
-    counter_max = int(args[args.index("--non-random-dither") + 1])
+    counter_max = args[args.index("--non-random-dither") + 1]
+    if counter_max == "auto":
+        counter_max = auto_counter_max(image.height)
+        print("Using non-random dither counter value of " + str(counter_max) + " pixels")
+    else:
+        counter_max = int(counter_max)
     if not dither:
         dither = auto_dither(bits)
         print("Non-random dither has no effect if dither is disabled. Guessing you want "+format_dither(dither)+" dither")
@@ -39,7 +50,6 @@ def binprecision(start, bits, length):
     while len(end) < bits:
         end = '0' + end
     return end[:length]
-image = PIL.Image.open(sys.argv[1])
 mode = "L" # 1x8 bit unsigned integer
 if per_color:
     mode = "RGB"
diff --git a/README.md b/README.md
index 928d2f2..3a2b61c 100644
--- a/README.md
+++ b/README.md
@@ -4,12 +4,12 @@ Inspired by [2bit](http://2bit.neocities.org/)
 
 Usage: `python3 2bit.py infile.png [outfile.png] [bits] [--per-color] [--dither dither_value] [--non-random-dither num_pixels]`
 
-dither\_value can be like `50%`, `50` or `.5`
+You can change the number of bits for different results. 1 would be just black and white, while 8 would be the original image in greyscale.
+
+dither\_value can be like `50%`, `50`, `.5` or `auto`
 
 Note that using `--non-random-dither` without a dither argument will attempt to guess what dither percentage you want based on the number of bits
 
-The best number for num\_pixels is usually 7, but it should ideally be coprime with the height of the image
+The best number for num\_pixels varies with the image. In general, the height of the image modulo num\_pixels + 1 should not equal zero. Experiment with it. Using `auto` will try to guess a good value such that you don't get horizontal bars, but it's not very good at it.
 
 Warning: Will probably turn transparency black
-
-You can change the number of bits for different results. 1 would be just black and white, while 8 would be the original image in greyscale.
diff --git a/test/run.py b/test/run.py
index f026c30..a5efe3c 100644
--- a/test/run.py
+++ b/test/run.py
@@ -8,8 +8,6 @@ files = glob.glob("*")
 del files[files.index("gentest.py")]
 del files[files.index("run.py")]
 if not os.path.isdir("out"): os.mkdir("out")
-i = 0
-max_i = len(files) * (112)
 def run(bits, percolor, dither, nonrandom):
     if not percolor:
         percolor = []
@@ -33,17 +31,21 @@ def run(bits, percolor, dither, nonrandom):
     outfilename = "out/" + ".".join(f.split(".")[:-1]) + "-output-" + pc + dc + nc + bits_formatted + "bits.png"
     print("On " + outfilename)
     subprocess.call(["python3", "../2bit.py", f, outfilename, bits_formatted, *percolor, *dither, *nonrandom])
-print(str(max_i) + " images to generate")
+torun = []
 for f in files:
     if (os.path.isdir(f)): continue
     if (f[-3:]) == '.py': continue
     for bits in range(8):
         for dither in [False, "15", "50", "auto"]:
-            for nonrandom in [False, "7", "10"]:
+            for nonrandom in [False, "7", "10", "auto"]:
                 for percolor in [False, True]:
                     if nonrandom and not dither: continue
-                    i += 1
-                    run(bits, percolor, dither, nonrandom)
-                    print(str(int(float(1000*i)/max_i)/10) + "% done")
+                    torun.append([bits, percolor, dither, nonrandom])
+print(str(len(torun)) + " images to generate")
+i = 0
+for args in torun:
+    i += 1
+    print(str(int(i * 1000 / len(torun))/10.0) + "% done")
+    run(*args)
 
 print("Done")